1. Field of the Invention
The invention relates to a plastic waveguide and more particularly to a plastic waveguide for guiding terahertz (THz) wave with a wavelength ranging from 30 to 3000 μm.
2. Description of the Prior Art
Strong attenuation in the terahertz (THz) gap, which occupies the wavelength ranging from 30 to 3000 μm (10 to 0.1 THz), is always a severe problem in long distance THz waveguiding. Even though many efforts on THz generation and detection techniques have been done to improve the detectable level of the THz signals, the unacceptably high dielectric loss and finite metal conductivity in this regime are still challenging optical fiber-type or metal-type waveguide design.
Hence, almost all the setups of current THz application systems are constructed with planar or curved metal reflectors, which make the system not only rigid but also vulnerable to environmental disturbance. With the perspective on a compact, reliable, and flexible THz system for applications such as molecular sensing, warfare inspections, and biomedical imaging, a low-loss THz waveguide is essential to be developed. Recently, many metal-based waveguiding techniques, including metal parallel plate and bare metal wire, were reported to have a much improved attenuation constant compared to other conventional microwave waveguides and various dielectric-based waveguides. The development of these low-attenuation metal waveguides has the potential to realize a waveguide-based THz system which usually requires a THz guiding distance longer than 1 meter. Even though the current reported results show that the metal-based guiding techniques are the best solutions that meet the need of low attenuation, we find that a simple plastic wire with a sub-wavelength diameter, similar to an optical fiber, can also provide a low guiding attenuation under the single-mode operation. The concept of such a sub-wavelength fiber has been successfully demonstrated both in the microwave and optical frequencies in 1940s and recent years, respectively.
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